0.3

This version causes major breaking API changes to simplify it and making it more intuitive.

• Improves testing by providing a test() contextmanager.
• Makes passing a naive datetime to instance() default to UTC.
• Reduces add_xxx()/sub_xxx() methods to add(**kwargs)/subtract(**kwargs).
• Changes the for_humans() method of the Interval class to in_words() to avoid confusion with the diff_for_humans() method.
• Makes more constants and methods available at module level.
• Makes the constructor behave like the standard one. No more Pendulum().
• Fixes "sl" locale.
• Renames the to() method to in_timezone().
• Removes the comparison methods to just stick with the basic operators.
• Reduces first_of_xxx()/last_of_xxx()/nth_of_xxx() methods to first_of(unit)/last_of(unit)/nth_of(unit, nth).
• Reduces start_of_xxx()/end_of_xxx() methods to start_of(unit)/end_of(unit).
• Removes the diff_in_xxx() methods from the Pendulum and adds in_xxx() methods to the Interval class.
• Renames the PendulumInterval class to simply Interval.
• Makes the Pendulum class immutable.